The gastrointestinal (GI) microbiota, or the gut probiotics as they are more commonly known, are the collection of microbes which live in our gut, essential for digestion, healthy metabolism as well as playing a crucial role in the development of our immune system. Our probiotics function as a major immunological organ and along with the gastrointestinal tract constitute about seventy percent of the immune system. If probiotic balance is disrupted, termed dysbiosis; harmful inflammation, autoimmunity and altered immune function occurs along with an increased risk of disease. In this state, the intestinal tract is particularly vulnerable to chronic conditions such as ulcerative colitis, Crohn’s disease, celiac disease and irritable bowel syndrome. Studies have also found links to systemic conditions such as obesity, type 1 and type 2 diabetes and many more highlighting the growing importance of GI microbiota to human health. Below the importance of probiotic supplementation in defending the GI microbiota from dysbiois will be shown.
The traditional belief was that the composition of GI microbiota was relatively stable from early childhood. However, overwhelming new evidence shows that diet, environmental and lifestyle factors such as stress can induce dysbiosis in GI microbiota. This was shown in studies on mice where diet was found to account for 57% of structural deviation in GI microbiota, with genetic difference only accounting for 12%. These findings further highlight the dominating role of diet in shaping GI microbiota. For example, the “Western” diet has been shown to induce dysbiois. Diets rich in complex carbohydrates show less pathogenic species than diets higher in fat or protein. Refined sugars, on the other hand, mediate the overgrowth of opportunistic bacteria and mould species.
A number of new studies have shown a positive effect of probiotic supplementation on immune health including allergies, prevention of respiratory disease and diarrhoea, particularly in children. In a study of 251 children supplementing with probiotics for 20 weeks resulted in fewer days with respiratory disorders as well as gastrointestinal (diarrhoea, vomiting, stomach pain and constipation) disorders, lower respiratory tract infections (32% vs. 49%) and fatigue (3% vs. 13%) in the probiotic group compared to placebo. In a review of 14 randomized controlled trials (RCTs) supplementing with probiotics had a positive effect both in diminishing the incidence of upper respiratory tract infections and the severity of the infection symptoms. While another review reported probiotics reduce the duration of illness in otherwise healthy children and adults.
Endurance athletes undergoing strenuous training are more susceptible to upper respiratory tract infection (URTI), believed to be due to the role of strenuous exercise in suppressing the immune system. In one study the number of days of symptoms of URTI was halved when the athletes took the probiotic, compared to placebo. The severity of the symptoms was also less when consuming probiotics.
Supplementing with probiotics has also been shown to be beneficial in reducing the incidence and severity of allergy symptoms. Changes in the composition of intestinal microflora play a central role in the development of allergic diseases. An Australian review with data covering over 2,000 infants from eight studies, concluded that supplementing with probiotics helps prevent eczema, other allergic diseases and food reactions in infants who might be susceptible, and showed benefits for a range of allergic diseases. They reported that probiotics helps prevent eczema in infants and one study suggested this benefit might last up to four years of age.
In Australia, Cow’s Milk Allergy (CMA) is the most common food allergy in children and is responsible for more than 40% of food-induced anaphylaxis in the childhood population. An increasing amount of evidence suggests the role of probiotics in prevention or treatment of CMA. In one study administration of probiotics to food-allergic children (age <2 years) improved the eczema and studies in infants with eczema who received probiotics showed benefits in decreasing gastrointestinal symptoms. Another study showed the benefits of supplementing with probiotics to reduce the symptoms of pollen allergy. In a study of approximately 200 mothers and their infants, expecting mothers taking probiotic supplements passed on immune benefits through the breast milk to the baby. Half of the mothers received probiotic supplements for four weeks prior to birth of their babies and these babies then receive the probiotics during the first year of life.